RABBAN (lit. "our teacher," "our master"):

Title given only to patriarchs, the presidents of the Sanhedrin. The first person to be called by this title was the patriarch Gamaliel I., ha-Zaḳen. The title was handed down from him to all succeeding patriarchs. According to Frankel ("Hodegetica in Mischnam," p. 58), Gamaliel I. received this title because he presided over the Sanhedrin alone without an ab bet din beside him, thus becoming the sole master. This derivation, however, is disproved by the fact that Gamaliel's father, Simon b. Hillel, was not called by that title, although he was the sole president of the Sanhedrin and had no ab bet din beside him. Another, still more improbable, explanation of the title is given by Brüll ("Einleitung in die Mischnah," i. 51). It is more likely that there was no special reasonfor the title, beyond the fact that the people loved and honored R. Gamaliel, and endeavored in this way to express their feeling (Weiss, "Dor," i. 179).